1. Field of the Invention
The present invention is in the field of medical electronics, and more specifically relates to an intelligent printer-plotter for presenting medical data in the form of printed tables and plotted graphs, and which is capable of smoothing the data by averaging it, and which further provides for editing of the data automatically and manually.
2. The Prior Art
In U.S. patent application Ser. No. 796,893 filed May 16, 1977, for Blood Pressure Monitoring System by Squires et al. there is described a portable device and a portable recorder to be worn by a patient to permit the measuring and recording of the patient's blood pressure and ECG signals over an extended period of time, such as 24 hours, as the patient engages in his daily program of activities. The value of such ambulatory monitoring is widely recognized and it is particularly useful when the symptoms are present only sporadically. Typically, in such a system, the systolic and diastolic blood pressures are measured at 7.5 minute intervals and recorded on a magnetic tape along with a continuous recording of the ECG signals.
The recorded tape is played back on an apparatus of the type disclosed in U.S. Pat. No. 4,073,011 issued Feb. 7, 1978, to Cherry et al. That playback device can be provided with a blood pressure data decoder and with a heart rate trend computer (as described in the aforementioned application of Squires et al.) to permit the blood pressure and heart rate data to be read from the magnetic tape and converted to a standardized signal format. The playback unit also produces timing signals in relation to the amount of tape played back, which permits the time of the various measurements to be determined. Thus, the playback unit provides as an output, time correlated data words representing values of systolic blood pressure, diastolic blood pressure and heart rate, along with timing signals. To be useful to a physician, these electrical signals must be reduced to a printed form such as a table or a graph.
It would, of course, be possible to use a printer or a charter of the kind known in the art to produce a table or chart of the raw data; unequestionably, such a graphical output would be helpful. However, upon reflection it can be seen that a simple printer or plotter is not the most desirable means for producing the graphical record. It is well known that intervention by the patient may cause fluctuations to appear in the raw data when the physiological variables are in fact substantially constant, and it is also known that some variability in the physiological variables is to be expected as the patient pursues his daily activities. In most applications, the physician is not concerned with these transient phenomena, but instead is interested in the longer-term variations. Thus, it would appear desirable to filter the data prior to plotting it to eliminate values which are clearly erroneous or impossible and to average the readings to eliminate the short-term fluctuations.